The inadequate treatment of municipal solid waste being put in landfills and the increasing addition of nondegradable materials, including plastics, to municipal solid waste streams are combining to drastically reduce the number of landfills available and to increase the costs of municipal solid waste disposal. While recycling of reusable components of the waste stream is desirable in many instances, the costs of recycling and the infrastructure required to recycle materials is sometimes prohibitive. In addition, there are some products which do not easily fit into the framework of recycling. The composting of non-recyclable solid waste is a recognized and growing method to reduce solid waste volume for landfilling and/or making a useful product from the waste to improve the fertility of fields and gardens. One of the limitations to marketing such compost is the visible contamination by undegraded plastic, such as film or fiber fragments.
It is thus desirable to provide components that are useful in disposable products and can be degraded into less contaminating forms under the conditions typically existing in waste composting processes. These conditions can include temperatures no higher than 70° C., and averaging in the 55-60° C. range; humid conditions as high as 100 percent relative humidity; and exposure times ranging from weeks to months. It is further desirable to provide disposable components that will not only degrade aerobically/anaerobically in composting, but will continue to degrade in soil or landfill. It is highly desirable that, in the presence of water, the components continue to break down into low molecular weight fragments that can be biodegraded by microorganisms into biogas, biomass, and liquid leachate, as occurs with natural organic materials such as wood.
Biodegradable films are known. For example, Wielicki, in U.S. Pat. No. 3,602,225, discloses the use of barrier films comprising plasticized, regenerated cellulose films. Comerford, et. al., in U.S. Pat. No. 3,952,347, disclose biodegradable films comprising a non-biodegradable matrix, such as poly(vinyl alcohol), and about 40 to 60 weight percent of a biodegradable materials, such as starch.
Biodegradable polyesters are known and can be grouped into three general classes; aliphatic polyesters, aliphatic-aromatic polyesters and sulfonated aliphatic-aromatic polyesters.
Aliphatic polyesters, as used herein, are polyesters derived solely from aliphatic dicarboxylic acids, such as poly(ethylene succinate) and poly(1,4-butylene adipate); and poly(hydroxyalkanates), such as polyhydroxybutyrate, polylactide, polycaprolactone, and polyglycolide. For example, Clendinning, et. al., in U.S. Pat. No. 3,932,319, disclose the use of biodegradable aliphatic polyesters, such as poly(ethylene adipate), in biodegradable blends, and Casey, et. al., in U.S. Pat. No. 4,076,798, discloses biodegradable resins derived from diglycolic acid and an unhindered glycol.
Aliphatic-aromatic polyesters, as used herein, include polyesters derived from a mixture of aliphatic dicarboxylic acids and aromatic dicarboxylic acids. For example, Sublett, in U.S. Pat. No. 4,419,507, discloses copolyesters derived from 100 mole percent of a dibasic acid component comprising 40-100 mole percent terephthalic acid and 0-60 mole percent of a second dicarboxylic acid containing 3-12 carbon atoms and 100 mole percent of glycol component comprising 40-100 mole percent 1,4-butanediol and 0-60 mole percent di(ethylene glycol), an example of which is a polyester prepared from 50 mole percent sebacic acid and 50 mole percent of terephthalic acid with 1,4-butanediol.
Films and coated substrates of aliphatic-aromatic polyesters are disclosed, for example, by Gallagher, et al., in U.S. Pat. No. 5,171,308; Warzelhan, et al., in U.S. Pat. No. 6,114,042 and U.S. Pat. No. 6,201,034. Examples of aliphatic-aromatic polyesters disclosed by Buchanan, et al., in U.S. Pat. No. 6,342,304 include poly(1,6-hexylene terephthalate-co-glutarate, (50:50, molar)), poly(1,4-butylene terephthalate-co-glutarate, (40:60, molar)), poly(1,4-butylene terephthalate-co-glutarate, (60:40, molar)), poly(1,4-butylene terephthalate-co-succinate, (30:70, molar)), (poly(1,4-butylene terephthalate-co-succinate, (15:85, molar)), poly(1,4-butylene-terephthalate-co-glutarate, (45:55, molar)), and poly(1,4-butylene terephthalate-co-glutarate-co-diglycolate, (45:50:5, molar)).
Sulfonated aliphatic-aromatic polyesters, as used herein, include polyesters derived from a mixture of aliphatic dicarboxylic acids and aromatic dicarboxylic acids and having incorporated therein a sulfonated monomer such as a salt of 5-sulfoisophthalic acid. Heilberger, in U.S. Pat. No. 3,563,942, discloses aqueous dispersions of solvent soluble linear sulfonated aliphatic-aromatic copolyesters including from 0.1 to 10 mole percent of the sulfonated aromatic monomer. Popp, et. al., in U.S. Pat. No. 3,634,541, discloses fiber-forming sulfonated aliphatic-aromatic copolyesters including 0.1 to 10 mole percent of xylylene sulfonated salt monomers. Kibler, et. al., in U.S. Pat. No. 3,779,993, discloses linear, sulfonated aliphatic-aromatic copolyesters including 2 to 12.5 mole percent of a sulfomonomer. Schade, in U.S. Pat. No. 4,104,262, disclose low molecular weight, water dispersible polyesters including 1-5 mole percent of an alkali metal-sulfonate group.
Films derived from sulfonated aliphatic-aromatic polyesters are known and are disclosed, for example, by Gallagher, et. al., in U.S. Pat. No. 5,171,308. Sulfonated aliphatic-aromatic polyester films filled with starch are also disclosed therein. Laminated substrates with sulfonated aliphatic-aromatic polyesters are also disclosed in U.S. Pat. No. 5,171,308.
Warzelhan, et. al., in U.S. Pat. No. 6,018,004, U.S. Pat. No. 6,114,042, and U.S. Pat. No. 6,201,034, disclose generally certain sulfonated aliphatic-aromatic copolyester compositions and their use in substrate coatings, films, and foams. However, there is no exemplification of compositions including the 1,3-propanediol disclosed herein and/or the surprisingly improved thermal properties of the compositions of the present invention.
Known biodegradable packaging materials typically include blends, and some published work in the area suggests that a single polymer does not have sufficient stability over wide temperature ranges for use in packaging. For example, the use of a single polymer or copolymer for use as packaging materials is disclosed as not advantageous by Khemani, et al., in WO 02/16468 A1.
Examples of known biodegradable materials for use in packaging include; EcoFoam®, a product of the National Starch Company of Bridgewater, N.J., which is a hydroxypropylated starch product, and EnviroFil®, a product of the EnPac Company, a DuPont-Con Agra Company. For example, Collinson, in U.S. Pat. No. 5,178,469, disclose the use of a cellulose film or cellophane on a Kraft paper for use of a collapsible biodegradable container, such as a bag, for liquid-containing solids. Tanner, et. al., in U.S. Pat. No. 5,213,858, disclose a biodegradable paperboard laminate structure consisting of a paperboard substrate, an exterior layer of a low temperature extrusion coatable, heat sealable biodegradable polymer, such as poly(vinyl alcohol) or starch, and an interior layer of a heat sealable, non-biodegradable polymer, such as polyethylene. The substrate can be used to produce, for example, cups, containers, and food packages. Franke, et. al., in U.S. Pat. No. 5,512,090, describe an extrudable biodegradable packaging material composed mainly of starch with vegetable oil, poly(vinyl alcohol), glycerin proteinaceous grain meal, glycerol monostearate, and optionally water. The compositions are disclosed to produce low density, foam substrate type products. Redd, et. al., in U.S. Pat. No. 6,106,753, disclose molded biodegradable articles from a mixture consisting of 80 to 90 percent of a starch and 20 to 10 weight percent of a biodegradable polymer. They further disclose the lamination of a biodegradable film onto the article. The use of biodegradable materials for packaging is also disclosed, for example, in U.S. Pat. No. 3,137,592, U.S. Pat. No. 4,673,438, U.S. Pat. No. 4,863,655, U.S. Pat. No. 5,035,930, U.S. Pat. No. 5,043,196 U.S. Pat. No. 5,095,054, U.S. Pat. No. 5,300,333, and U.S. Pat. No. 5,413,855.
Although aliphatic-aromatic copolyester and sulfonated aliphatic-aromatic copolyester compositions and their use in forming films, coatings, and laminates, and the use thereof in, for example, fast food disposable packaging is known, improved properties in such copolyesters are desired. Exemplary disclosures of such copolyesters and their use include Gallagher, et. al., in U.S. Pat. No. 5,171,308, U.S. Pat. No. 5,171,309, and U.S. Pat. No. 5,219,646, the disclosures of Buchanan, et al., in U.S. Pat. No. 5,446,079 and U.S. Pat. No. 6,342,304, and the disclosures of Warzelhan, et al., in U.S. Pat. No. 5,936,045, U.S. Pat. No. 6,018,004, U.S. Pat. No. 6,046,248, U.S. Pat. No. 6,114,042, U.S. Pat. No. 6,201,034, U.S. Pat. No. 6,258,924 and U.S. Pat. No. 6,297,347. Typically, the sulfonated aliphatic-aromatic copolyesters based on ethylene glycol tend to have greater crystalline melting points than those based on 1,4-butanediol, but can have relatively low crystallinity and crystallization rates, especially when they contain relatively larger ratios of an aliphatic dicarboxylic acid component. On the other hand, the known sulfonated aliphatic-aromatic copolyesters based on 1,4-butanediol tend to have good crystallinity and crystallization rates, but suffer from lower crystalline melting points, especially those containing greater amounts of an aliphatic dicarboxylic acid component. Moreover, some such sulfonated aliphatic-aromatic copolyesters do not provide sufficient or optimal temperature characteristics, such as crystalline melting point, crystallinity and crystallization rate, for such significant end uses such as film, coatings and laminates.
The present invention provides sulfonated aliphatic-aromatic copolyesters derived from 1,3-propanediol and sebacic acid. The sulfonated aliphatic-aromatic copolyesters disclosed herein provide improved thermal properties in comparison with some known copolyesters. In particular, the sulfonated aliphatic-aromatic copolyesters disclosed herein provide a desirable balance of high temperature properties not disclosed for known aliphatic-aromatic copolyesters and improved compostability.
While blends have been used in order to obtain a desirable balance of physical and/or thermal properties in polyesters, as disclosed, for example, in WO 02/16468 A1, as one skilled in the art will appreciate, the use of polymeric blends necessarily complicates the processes used to produce the film, coating, and laminates. The present invention eliminates the need to utilize blends and provides sulfonated aliphatic-aromatic copolyesters having optimized thermal and physical properties. However, blends containing the sulfonated aliphatic-aromatic copolyesters disclosed herein are within the scope of the present invention.